Chemical Loss Rates Research Articles

Substantial loss of isoprene in the surface ocean due to chemical and biological consumption

Isoprene contributes to the formation of ozone and secondary organic aerosol in the atmosphere, and thus influences cloud albedo and climate. Isoprene is ubiquitous in the surface open ocean where it is produced by phytoplankton, however emissions from the global ocean are poorly constrained, in part due to a lack of knowledge of oceanic sink or degradation terms. Here, we present analyses of ship-based seawater incubation experiments with samples from the Mediterranean, Atlantic, tropical Pacific and circum-Antarctic and Subantarctic oceans to determine chemical and biological isoprene consumption in the surface ocean. We find the total isoprene loss to be comprised of a constant chemical loss rate of 0.05 ± 0.01 d−1 and a biological consumption rate that varied between 0 and 0.59 d−1 (median 0.03 d−1) and was correlated with chlorophyll-a concentration. We suggest that isoprene consumption rates in the surface ocean are of similar magnitude or greater than ventilation rates to the atmosphere, especially in chlorophyll-a rich waters.

DOES PROLONGED ESTRACE ADMINISTRATION EFFECT ON PREGNANCY OUTCOME IN PROGRAMMED FROZEN EMBRYO TRANSFER CYCLE?

To determine whether women in frozen-thawed embryo transfer (FET) cycles, who continued prolonged estrogen administration beyond the standard 12 days due to a thin endometrial stripe exhibited lower pregnancy rates. We retrospectively analyzed the outcomes of 822 FET cycles from January 1, 2019 through March 1, 2021. Oocyte recipients or women with known intrauterine adhesions were excluded. Women received twelve days of 6 mg of oral 17 beta Estradiol (Estrace) after ovarian suppression was confirmed. If after twelve days of Estrace their endometrial stripe (ES) was equal to or less than 7 mm, then their estrogen regimen was continued until her ES was at least 7mm. Intramuscular progesterone 50mg intramuscularly was then administered and a single thawed blastocyst was transferred 132 hours later. Variables assessed included thickens of endometrium, pregnancy (serum hCG), clinical pregnancy, and implantation rate by fetal cardiac activity and pregnancy outcome. The Fisher’s Exact Test and t-test were used. A p value <0.05 was considered significant. Twenty three of 822 cycle were continued on their estrogen regimen to meet ES criteria for at least five days (range 5 to 14 days). No significant differences in age, prior failed FET cycles, and percentage of euploid blastocysts were noted between those women who did or did not requires at least five days more of exogenous estrogen. However, endometrial thickness was significantly thicker in regular FET group compared that of pushed FET cycle at day 12 (9.59 mm vs 6.16 mm, p<0.05). Furthermore, their thin endometrial thickness was significantly improved after prolonged Estrace (6.16 mm vs 7.49 mm, p<0.05). Among pushed FET cycles, five patients were pushed for 14 days and the endometrial thickness were improved from 4.78 mm to 7.08 mm (p=0.11). The pregnancy rate (positive serum hCG/total transfers), clinical pregnancy rates and implantation rate were not significantly different between regular and pushed FET cycles (73.2 %vs 75.0 %), (68.8 % vs 62.5 %), and (59.4 % vs 52.0 %), respectively. The pregnancy outcomes in two groups were similar by age group or PGT performed group. Additionally, chemical pregnancy loss or miscarriage rate did not differ between two groups (7 % vs 4%) and (7 % vs 4 %), respectively. Ongoing pregnancy/live birth rate was 60.9 % (14/23) for regular FET and 59.7 % (462/799) for pushed FET. Our findings suggest that continued exogenous estrogen administration successfully increased the endometrial thickness in all patients with a thin ES and did not adversely affect pregnancy outcome.

Understanding isoprene photooxidation using observations and modeling over a subtropical forest in the southeastern US

Abstract. The emission, dispersion, and photochemistry of isoprene (C5H8) and related chemical species in the convective boundary layer (CBL) during sunlit daytime were studied over a mixed forest in the southeastern United States by combining ground-based and aircraft observations. Fluxes of isoprene and monoterpenes were quantified at the top of the forest canopy using a high-resolution proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). Snapshot (∼ 2 min sampling duration) vertical profiles of isoprene, methyl vinyl ketone (MVK) + methacrolein (MACR), and monoterpenes were collected from aircraft every hour in the CBL (100–1000 m). Both ground-based and airborne collected volatile organic compound (VOC) data are used to constrain the initial conditions of a mixed-layer chemistry model (MXLCH), which is applied to examine the chemical evolution of the O3–NOx–HOx–VOC system and how it is affected by boundary layer dynamics in the CBL. The chemical loss rate of isoprene (∼ 1 h) is similar to the turbulent mixing timescale (0.1–0.5 h), which indicates that isoprene concentrations are equally dependent on both photooxidation and boundary layer dynamics. Analysis of a model-derived concentration budget suggests that diurnal evolution of isoprene inside the CBL is mainly controlled by surface emissions and chemical loss; the diurnal evolution of O3 is dominated by entrainment. The NO to HO2 ratio (NO : HO2) is used as an indicator of anthropogenic impact on the CBL chemical composition and spans a wide range (1–163). The fate of hydroxyl-substituted isoprene peroxyl radical (HOC5H8OO·; ISOPOO) is strongly affected by NO : HO2, shifting from NO-dominant to NO–HO2-balanced conditions from early morning to noontime. This chemical regime change is reflected in the diurnal evolution of isoprene hydroxynitrates (ISOPN) and isoprene hydroxy hydroperoxides (ISOPOOH).

Transport and chemical loss rates in Saturn's inner plasma disk

AbstractThe Kronian moon Enceladus is constantly feeding its surrounding with new gas and dust, from cryovolcanoes located in its south polar region. Through photoionization and impact ionization of these neutrals, a plasma disk is created, which mainly contains hydrogen ions and water group ions. This paper investigates the importance of ion loss by outward radial transport and ion loss by dissociative recombination, which is the dominant chemical loss process in the inner plasma disk. We use plasma densities derived from several years of measurements by the Cassini Radio and Plasma Wave Science electric field power spectral density and Langmuir probe to calculate the total flux tube content NL2. Our calculation shows that NL2 agrees well with earlier estimates within dipole L shell 8. We also show that loss by transport dominates chemical loss between L shells 4 and 10. Using extrapolation of available measurements, we extend the study to include L shells 2.5 to 4. The results indicate that loss by transport dominates chemical loss also between L shells 2.5 and 4. The loss rate by transport is around five times larger at L shell 5, and the difference increases as L7.7 beyond L = 5, for the net ion population. Chemical loss may still be important for the structure of the plasma disk in the region closest to Enceladus (around ±0.5 RS) at 3.95 RS (1 RS = Saturn's equatorial radius = 60,268 km), since the transport and chemical loss rates only differ by a factor of ∼2 in this region. We also derive the total plasma content of the plasma disk between L shells 4 and 10 to be 1.9 × 1033 ions and the total ion source rate for the same region to be 5.8 × 1027 s−1. The estimated equatorial ion production rate P ranges from 2.6 × 10−5 cm−3 s−1 (at L = 10) to 1.1 × 10−4 cm−3 s−1 (at L = 4.8). The net mass loading rate is derived to be 123 kg/s for L shells 4 to 10.

Deep weathering along a granite ridgeline in a subtropical climate

Bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11-meter profile weathering on a granite ridgeline under subtropical climate conditions in south China. The weathering sequence is delineated by mineralogy and major element variations. Apatite, biotite, hornblende and plagioclase dissolve early during weathering, resulting in nearly 100% Ca and Na loss and significant Mg, Fe and P depletion at depth. The K-feldspar reaction front begins at the depth of depletion of plagioclase, leading to a loss of ~80% of the K at the land surface near the bottom of the ridgeline and almost 100% at the top. Dissolution of quartz and other silicates releases about 60% of Si in the profiles. Kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer. The soil horizon (upper 100cm) is the zone dominated by pedogenic processes, including active biological activity, physical erosion and influx of high concentrations of atmospheric components (especially CO2 and O2). The pedogenic processes are characterized by low pH (~4.54 to 5.85), high clay content (kaolinite: 6–16wt.%; gibbsite: 2–8wt.%) and total organic carbon content (0.13–3.93%) and intensive fracturing and dissolution of quartz and K-feldspar compared with the lower horizons.Accumulation of organic material and resistant minerals downslope is attributed to down-ridge movement of water (termed here, interflow) and weathering products in the uppermost 100cm down the ridgeline. Using a mass balance model calculation for the catena that assumes steady-state soil thickness at all sites, the bottom profile shows the highest apparent total chemical weathering loss rate (~14gm−2y−1) whereas the middle position shows the highest physical erosion loss rate (~44gm−2y−1). SiO2 accounts for about 84% of the chemical weathering outflux from the soil horizons along the ridgeline hillslope. Chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite.This study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena.

Influence of geomagnetic storms of September 26–30, 2011, on the ionosphere and HF radiowave propagation. I. Ionospheric effects

Geomagnetic storm ionospheric effects observed at different latitudes and longitudes on September 26 and 28–30, 2011, are interpreted with the GSM TIP model. It has been justified that the results of this model can subsequently be used to calculate the HF radiowave ray tracing under quiet conditions and for the selected dates in September 2011. The model calculations are compared with observations of the ionospheric parameters performed by different radiophysical methods. The presented results confirm the classical mechanisms by which positive and negative ionospheric storms are formed during the main phase of a geomagnetic storm. At high latitudes, the electron density is mainly disturbed due to changes in the neutral composition of the thermosphere, resulting in an increase in the chemical loss rates, and the electromagnetic drift, which results in a substantial reconstruction of the high-latitude ionosphere owing to the horizontal plasma transfer. During the storm recovery phase at midlatitudes, electron density positive disturbances are formed in the daytime due to an increase in the n(O)/n(N2) ratio; at the same time, negative effects in the electron density are formed at night as a result of plasma tube devastation. Comparison with the observations indicates that the presented model calculation results can be used to describe a medium for solving problems of radiowave propagation in the ionosphere during the storm main phase on September 26 and during the recovery phase on September 28–30, 2011.

Simulation of atmospheric N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O with GEOS-Chem and its adjoint: evaluation of observational constraints

Abstract. We describe a new 4D-Var inversion framework for nitrous oxide (N2O) based on the GEOS-Chem chemical transport model and its adjoint, and apply it in a series of observing system simulation experiments to assess how well N2O sources and sinks can be constrained by the current global observing network. The employed measurement ensemble includes approximately weekly and quasi-continuous N2O measurements (hourly averages used) from several long-term monitoring networks, N2O measurements collected from discrete air samples onboard a commercial aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container; CARIBIC), and quasi-continuous measurements from the airborne HIAPER Pole-to-Pole Observations (HIPPO) campaigns. For a 2-year inversion, we find that the surface and HIPPO observations can accurately resolve a uniform bias in emissions during the first year; CARIBIC data provide a somewhat weaker constraint. Variable emission errors are much more difficult to resolve given the long lifetime of N2O, and major parts of the world lack significant constraints on the seasonal cycle of fluxes. Current observations can largely correct a global bias in the stratospheric sink of N2O if emissions are known, but do not provide information on the temporal and spatial distribution of the sink. However, for the more realistic scenario where source and sink are both uncertain, we find that simultaneously optimizing both would require unrealistically small errors in model transport. Regardless, a bias in the magnitude of the N2O sink would not affect the a posteriori N2O emissions for the 2-year timescale used here, given realistic initial conditions, due to the timescale required for stratosphere–troposphere exchange (STE). The same does not apply to model errors in the rate of STE itself, which we show exerts a larger influence on the tropospheric burden of N2O than does the chemical loss rate over short (&lt; 3 year) timescales. We use a stochastic estimate of the inverse Hessian for the inversion to evaluate the spatial resolution of emission constraints provided by the observations, and find that significant, spatially explicit constraints can be achieved in locations near and immediately upwind of surface measurements and the HIPPO flight tracks; however, these are mostly confined to North America, Europe, and Australia. None of the current observing networks are able to provide significant spatial information on tropical N2O emissions. There, averaging kernels (describing the sensitivity of the inversion to emissions in each grid square) are highly smeared spatially and extend even to the midlatitudes, so that tropical emissions risk being conflated with those elsewhere. For global inversions, therefore, the current lack of constraints on the tropics also places an important limit on our ability to understand extratropical emissions. Based on the error reduction statistics from the inverse Hessian, we characterize the atmospheric distribution of unconstrained N2O, and identify regions in and downwind of South America, central Africa, and Southeast Asia where new surface or profile measurements would have the most value for reducing present uncertainty in the global N2O budget.

Seasonal variability of methyl iodide in the Kiel Fjord

From October 2008 to November 2010, CH3I concentrations were measured in the Kiel Fjord together with potentially related biogeochemical and physical parameters. A repeating seasonal cycle of CH3I was observed with highest concentrations in summer (ca. 8.3 pmol L−1; June and July) and lowest concentrations in winter (ca. 1.5 pmol L−1; December to February). A strong positive correlation at zero lag between [CH3I] and solar radiation (R2 = 0.93) was observed, whereas correlations with other variables (SST, Chlorophyll a) were weaker, and they lagged CH3I by ca. 1 month. These results appear consistent with the hypothesis that SSR is the primary forcing of CH3I production in surface seawater, possibly through a photochemical pathway. A mass balance of the monthly averaged data was used to infer mean rates of daily net production (Pnet) and losses for CH3I over the year. The sea-to-air flux of CH3I in the Kiel Fjord averaged 3.1 nmol m−2 d−1, the mean chemical loss rate was 0.047 pmol L−1 d−1, and Pnet varied systematically from winter to summer (from 0 to 0.6 pmol L−1 d−1). Pnet was correlated at zero lag with SST, SSR, and Chla (R2 = 0.55, 0.67, and 0.73, respectively, p << 0.01). The lagged cross-correlation analysis indicated that SSR led Pnet by 1 month, whereas the strongest cross correlations with Chla were at lags of 0 to +1 month, and SST lagged Pnet by 1 month. The broad seasonal peak of Pnet makes it difficult to determine the key factor controlling CH3I net production using in situ concentration data alone.

Observations of a seasonal cycle in NOx emissions from fires in African woody savannas

Nitrogen oxide (NOx) emissions from wildfires account for ~15% of the global total, inducing large fluctuations in the chemical production and loss rates of O3 and CH4 and thereby affecting Earth's radiative balance. NOx emissions from fires depend on fuel nitrogen (N) content, the relative contributions of flaming and smoldering combustion, and total biomass burned. Current understanding of the variability in these factors across biomes is limited by sparse observations. Here we use satellite‐based measurements to study emission coefficients (ECs), a value proportional to NOx emitted per unit of biomass burned, from fires in African savannas. We show that ECs for NOx exhibit a pronounced seasonal cycle in woody savannas, with early‐season ECs 20–40% above and late‐season ECs 30–40% below the mean, while no cycle exists in nonwoody savannas. We discuss several possible mechanisms of the observed cycle including seasonal differences in fuel N content and modified combustion efficiency.

Evaluation of HO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; sources and cycling using measurement-constrained model calculations in a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated ecosystem

Abstract. We present a detailed analysis of OH observations from the BEACHON (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen)-ROCS (Rocky Mountain Organic Carbon Study) 2010 field campaign at the Manitou Forest Observatory (MFO), which is a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated forest environment. A comprehensive suite of measurements was used to constrain primary production of OH via ozone photolysis, OH recycling from HO2, and OH chemical loss rates, in order to estimate the steady-state concentration of OH. In addition, the University of Washington Chemical Model (UWCM) was used to evaluate the performance of a near-explicit chemical mechanism. The diurnal cycle in OH from the steady-state calculations is in good agreement with measurement. A comparison between the photolytic production rates and the recycling rates from the HO2 + NO reaction shows that recycling rates are ~20 times faster than the photolytic OH production rates from ozone. Thus, we find that direct measurement of the recycling rates and the OH loss rates can provide accurate predictions of OH concentrations. More importantly, we also conclude that a conventional OH recycling pathway (HO2 + NO) can explain the observed OH levels in this non-isoprene environment. This is in contrast to observations in isoprene-dominated regions, where investigators have observed significant underestimation of OH and have speculated that unknown sources of OH are responsible. The highly-constrained UWCM calculation under-predicts observed HO2 by as much as a factor of 8. As HO2 maintains oxidation capacity by recycling to OH, UWCM underestimates observed OH by as much as a factor of 4. When the UWCM calculation is constrained by measured HO2, model calculated OH is in better agreement with the observed OH levels. Conversely, constraining the model to observed OH only slightly reduces the model-measurement HO2 discrepancy, implying unknown HO2 sources. These findings demonstrate the importance of constraining the inputs to, and recycling within, the ROx radical pool (OH + HO2 + RO2).

Evaluation of factors controlling global secondary organic aerosol production from cloud processes

Abstract. Secondary organic aerosols (SOA) exert a significant influence on ambient air quality and regional climate. Recent field, laboratorial and modeling studies have confirmed that in-cloud processes contribute to a large fraction of SOA production with large space-time heterogeneity. This study evaluates the key factors that govern the production of cloud-process SOA (SOAcld) on a global scale based on the GFDL coupled chemistry-climate model AM3 in which full cloud chemistry is employed. The association between SOAcld production rate and six factors (i.e., liquid water content (LWC), total carbon chemical loss rate (TCloss), temperature, VOC/NOx, OH, and O3) is examined. We find that LWC alone determines the spatial pattern of SOAcld production, particularly over the tropical, subtropical and temperate forest regions, and is strongly correlated with SOAcld production. TCloss ranks the second and mainly represents the seasonal variability of vegetation growth. Other individual factors are essentially uncorrelated spatiotemporally to SOAcld production. We find that the rate of SOAcld production is simultaneously determined by both LWC and TCloss, but responds linearly to LWC and nonlinearly (or concavely) to TCloss. A parameterization based on LWC and TCloss can capture well the spatial and temporal variability of the process-based SOAcld formation (R2 = 0.5) and can be easily applied to global three dimensional models to represent the SOA production from cloud processes.

Ozone loss rates in the Arctic winter stratosphere during 1994-2000 derived from POAM II/III and ILAS observations: Implications for relationships among ozone loss, PSC occurrence, and temperature

[1] Quantitative chemical ozone loss rates at the 475 K isentropic surface inside the Arctic polar vortex are evaluated for six winters (January through March) using a satellite-based Match technique. Satellite observational data are taken from the Polar Ozone and Aerosol Measurement (POAM) II for 1994–1996, the Improved Limb Atmospheric Spectrometer (ILAS) for 1997, and the POAM III for 1999–2000. The largest ozone loss rates were observed in the end of January 1995 (∼50 ± 20 ppbv d−1), February 1996 (∼40–50 ± 15 ppbv d−1), February 1997 (∼40 ± 8 ppbv d−1), January 2000 (∼60 ± 30 ppbv d−1), and early March 2000 (∼40 ± 10 ppbv d−1). The probability of polar stratospheric cloud (PSC) existence is estimated using aerosol extinction coefficient data from POAM II/III and ILAS. Ozone loss and the PSC probability are strongly correlated and an absolute increase of 10% in the PSC probability is found to amplify the chemical ozone loss rate during Arctic winter by approximately 25 ± 6 ppbv per day or 3.2 ± 0.7 ppbv per sunlit hour. Relationships between average Arctic winter ozone loss rates and various PSC- and temperature-related indices are investigated, including the area of polar vortex that is colder than the threshold temperature for PSC existence (APSC), the PSC formation potential (PFP), and the potential for activation of chlorine (PACl). Of these three, PACl provides the best proxy representation of interannual variability in Arctic ozone loss at the 475 K level. Large ozone loss occurred primarily for air masses that experienced low temperatures between 187 K and 195 K within the previous 10 days and the ozone loss rates clearly increase with decreasing the minimum temperature. The particularly large ozone losses of ∼9 ± 3 ppbv per sunlit hour in February 1996 and January 2000 were associated with low minimum temperatures of 187–189 K, simultaneously with high PSC probabilities.

A budget analysis of NO x column losses over the Korean peninsula

In this study, the chemical and physical losses of nitrogen oxides (NOx) over the Korean peninsula were discussed in order to better understand the effects of the NOx losses on the tropospheric NO2 columns. Initially, it was found that the physical loss processes due to dry and wet depositions had almost negligible impacts on the NOx loss processes over the Korean peninsula. In contrast, the hourly NOx chemical column losses were large at ∼1014 molecules cm−2 h−1. The amounts of NOx removed for 1 hour account for approximately 33–35% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. The NOx chemical column loss rates were 24.1–70.9 times larger than the NOx physical column loss rates. In a budget analysis of the NOx chemical column losses, HNO3 formation via the reaction of OH + NO2 had the largest contribution toward the NOx chemical losses (42–55% during fall and winter seasons; 76–77% during spring; 92–93% during summer). Large amounts of NOx were also removed by heterogeneous nitrate formation via N2O5 condensation during the cold seasons (42–56%) over the Korean peninsula. The columnar NOx chemical losses took place mainly due to the two chemico-physical reaction processes, and also showed seasonal variations. PAN (Peroxyacetyl Nitrate) is another NO2 reservoir of potential importance. If the influence of the PAN-related chemistry on the NOx budget is considered, it can result in an approximate 69% increase in the NOx chemical column loss during summer. Such increases in the amounts of NOx removed for 1 hour due to the formation of PAN were equivalent to 56–58% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. Such active NOx chemical losses during summer are another main factor for the tropospheric NO2 columns exhibiting their smallest values during summer.

A model study of the impact of source gas changes on the stratosphere for 1850–2100

Abstract. The long-term stratospheric impacts due to emissions of CO2, CH4, N2O, and ozone depleting substances (ODSs) are investigated using an updated version of the Goddard two-dimensional (2-D) model. Perturbation simulations with the ODSs, CO2, CH4, and N2O varied individually are performed to isolate the relative roles of these gases in driving stratospheric changes over the 1850–2100 time period. We also show comparisons with observations and the Goddard Earth Observing System chemistry-climate model simulations for the time period 1960–2100 to illustrate that the 2-D model captures the basic processes responsible for long-term stratospheric change. The ODSs, CO2, CH4, and N2O impact ozone via several mechanisms. ODS and N2O loading decrease stratospheric ozone via the increases in atmospheric halogen and odd nitrogen species, respectively. CO2 loading impacts ozone by: (1) cooling the stratosphere which increases ozone via the reduction in the ozone chemical loss rates, and (2) accelerating the Brewer-Dobson circulation (BDC) which redistributes ozone in the lower stratosphere. The net result of CO2 loading is an increase in global ozone in the total column and upper stratosphere. CH4 loading impacts ozone by: (1) increasing atmospheric H2O and the odd hydrogen species which decreases ozone via the enhanced HOx-ozone loss rates; (2) increasing the H2O cooling of the middle atmosphere which reduces the ozone chemical loss rates, partially offsetting the enhanced HOx-ozone loss; (3) converting active to reservoir chlorine via the reaction CH4+Cl→HCl+CH3 which leads to more ozone; and (4) increasing the NOx-ozone production in the troposphere. The net result of CH4 loading is an ozone decrease above 40–45 km, and an increase below 40–45 km and in the total column. The 2-D simulations indicate that prior to 1940, the ozone increases due to CO2 and CH4 loading outpace the ozone losses due to increasing N2O and carbon tetrachloride (CCl4) emissions, so that total column and upper stratospheric global ozone reach broad maxima during the 1920s–1930s. This precedes the significant ozone depletion during ~1960–2050 driven by the ODS loading. During the latter half of the 21st century as ODS emissions diminish, CO2, N2O, and CH4 loading will all have significant impacts on global total ozone based on the Intergovernmental Panel on Climate Change (IPCC) A1B (medium) scenario, with CO2 having the largest individual effect. Sensitivity tests illustrate that due to the strong chemical interaction between methane and chlorine, the CH4 impact on total ozone becomes significantly more positive with larger ODS loading. The model simulations also show that changes in stratospheric temperature, BDC, and age of air during 1850–2100 are controlled mainly by the CO2 and ODS loading. The simulated acceleration of the BDC causes the global average age of air above 22 km to decrease by ~1 yr from 1860–2100. The photochemical lifetimes of N2O, CFCl3, CF2Cl2, and CCl4 decrease by 11–13 % during 1960–2100 due to the acceleration of the BDC, with much smaller lifetime changes (&lt;4 %) caused by changes in the photochemical loss rates.

Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles

Abstract. Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles approximating atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant timescales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

Deposition of dinitrogen pentoxide, N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;5&amp;lt;/sub&amp;gt;, to the snowpack at high latitudes

Abstract. Dinitrogen pentoxide, N2O5, is an important nighttime intermediate in the oxidation of NOx that is hydrolysed on surfaces. We conducted a field campaign in Fairbanks, Alaska during November 2009 to measure the gradient and derive a flux (and deposition velocity) of N2O5 depositing to snowpack using the aerodynamic gradient method. The deposition velocity of N2O5 under Arctic winter conditions was found to be 0.59 ± 0.47 cm s−1, which is the first measurement of this parameter to our knowledge. Based on the measured deposition velocity, we compared the chemical loss rate of N2O5 via snowpack deposition to the total steady state loss rate and found that deposition to snowpack is at least 1/8th of the total chemical removal of N2O5 that is located within the first few meters above the ground surface.

Vertical transport rates and concentrations of OH and Cl radicals in the Tropical Tropopause Layer from observations of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and halocarbons: implications for distributions of long- and short-lived chemical species

Abstract. Rates for large-scale vertical transport of air in the Tropical Tropopause Layer (TTL) were determined using high-resolution, in situ observations of CO2 concentrations in the tropical upper troposphere and lower stratosphere during the NASA Tropical Composition, Cloud and Climate Coupling (TC4) campaign in August 2007. Upward movement of trace gases in the deep tropics was notably slower in TC4 than during the Costa Rica AURA Validation Experiment (CR-AVE), in January 2006. Transport rates in the TTL were combined with in situ measurements of chlorinated and brominated organic compounds from whole air samples to determine chemical loss rates for reactive chemical species, providing empirical vertical profiles for 24-h mean concentrations of hydroxyl radicals (OH) and chlorine atoms in the TTL. The analysis shows that important short-lived species such as CHCl3, CH2Cl2, and CH2Br2 have longer chemical lifetimes than the time for transit of the TTL, implying that these species, which are not included in most models, could readily reach the stratosphere and make significant contributions of chlorine and/or bromine to stratospheric loading.

Clouds, photolysis and regional tropospheric ozone budgets

Abstract. We use a three-dimensional chemical transport model to examine the shortwave radiative effects of clouds on the tropospheric ozone budget. In addition to looking at changes in global concentrations as previous studies have done, we examine changes in ozone chemical production and loss caused by clouds and how these vary in different parts of the troposphere. On a global scale, we find that clouds have a modest effect on ozone chemistry, but on a regional scale their role is much more significant, with the size of the response dependent on the region. The largest averaged changes in chemical budgets (±10–14%) are found in the marine troposphere, where cloud optical depths are high. We demonstrate that cloud effects are small on average in the middle troposphere because this is a transition region between reduction and enhancement in photolysis rates. We show that increases in boundary layer ozone due to clouds are driven by large-scale changes in downward ozone transport from higher in the troposphere rather than by decreases in in-situ ozone chemical loss rates. Increases in upper tropospheric ozone are caused by higher production rates due to backscattering of radiation and consequent increases in photolysis rates, mainly J(NO2). The global radiative effect of clouds on isoprene, through decreases of OH in the lower troposphere, is stronger than on ozone. Tropospheric isoprene lifetime increases by 7% when taking clouds into account. We compare the importance of clouds in contributing to uncertainties in the global ozone budget with the role of other radiatively-important factors. The budget is most sensitive to the overhead ozone column, while surface albedo and clouds have smaller effects. However, uncertainty in representing the spatial distribution of clouds may lead to a large sensitivity of the ozone budget components on regional scales.

Investigation of NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; emissions and NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;-related chemistry in East Asia using CMAQ-predicted and GOME-derived NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; columns

Abstract. In this study, NO2 columns from the US EPA Models-3/CMAQ model simulations carried out using the 2001 ACE-ASIA (Asia Pacific Regional Aerosol Characterization Experiment) emission inventory over East Asia were compared with the GOME-derived NO2 columns. There were large discrepancies between the CMAQ-predicted and GOME-derived NO2 columns in the fall and winter seasons. In particular, while the CMAQ-predicted NO2 columns produced larger values than the GOME-derived NO2 columns over South Korea for all four seasons, the CMAQ-predicted NO2 columns produced smaller values than the GOME-derived NO2 columns over North China for all seasons with the exception of summer (summer anomaly). It is believed that there might be some error in the NOx emission estimates as well as uncertainty in the NOx chemical loss rates over North China and South Korea. Regarding the latter, this study further focused on the biogenic VOC (BVOC) emissions that were strongly coupled with NOx chemistry during summer in East Asia. This study also investigated whether the CMAQ-modeled NO2/NOx ratios with the possibly overestimated isoprene emissions were higher than those with reduced isoprene emissions. Although changes in both the NOx chemical loss rates and NO2/NOx ratios from CMAQ-modeling with the different isoprene emissions affected the CMAQ-modeled NO2 levels, the effects were found to be limited, mainly due to the low absolute levels of NO2 in summer. Seasonal variations of the NOx emission fluxes over East Asia were further investigated by a set of sensitivity runs of the CMAQ model. Although the results still exhibited the summer anomaly possibly due to the uncertainties in both NOx-related chemistry in the CMAQ model and the GOME measurements, it is believed that consideration of both the seasonal variations in NOx emissions and the correct BVOC emissions in East Asia are critical. Overall, it is estimated that the NOx emissions are underestimated by ~57.3% in North China and overestimated by ~46.1% in South Korea over an entire year. In order to confirm the uncertainty in NOx emissions, the NOx emissions over South Korea and China were further investigated using the ACE-ASIA, REAS (Regional Emission inventory in ASia), and CAPSS (Clean Air Policy Support System) emission inventories. The comparison between the CMAQ-calculated and GOME-derived NO2 columns indicated that both the ACE-ASIA and REAS inventories have some uncertainty in NOx emissions over North China and South Korea, which can also lead to some errors in modeling the formation of ozone and secondary aerosols in South Korea and North China.

The critical solar wind pressure for IMF penetration into the Venus ionosphere

Early observations and simulations have revealed that the occurrence of IMF penetration into the Venus ionosphere depends on the upstream solar wind pressure, and that IMF is transported into the ionosphere by the downward convection when the solar wind dynamic pressure is relatively large. In this paper, we investigated the critical solar wind pressure for the IMF penetration, by using a two‐dimensional global MHD model. The simulations showed that variations in the upstream solar wind pressure (PSW) affect plasma dynamics and chemistry in the subsolar ionosphere. The chemical plasma loss rate increases as PSW increases, and the amount of plasma loss exceeds that of plasma production when PSW exceeds a certain critical level (Pcrtc). On this occasion, the plasma convection in the ionosphere connects to the solar wind flow, and as a result the connected downward convection transports IMF into the ionosphere. The simulations also showed that IMF penetration occurs only when PSW exceeds Pcrtc, even if the solar wind pressure changes abruptly. The critical pressure is not necessarily equal to the ionospheric peak thermal pressure (Ppeak). Our simulations suggested that Pcrtc is smaller than Ppeak.